Battery tender is well worth the few bucks. Odyssey battery rep told me to use one year round. He said it takes approx. 50 miles of continuous riding to fully charge a battery. Still have my OEM battery in my 08 Streetglide, and it cranks the 120R with no problem.
For me it depends on the how the bike was used before it went back in the garage. Lots of short runs or a stop for gas just before coming home, it goes on the tender. If it is a 40 mile or more uninterrupted run, then the maintainer isn't as vital to bring the battery back to full charge as the trip was long enough to do that.
My bike stays on the tender if its going to be parked for a few days or longer. My 06 1200 sporty came with the tender when I bought the bike, my Limited did not, go figure, lmao.....